public final class Entreprise {
    Map<String, Service> services = new HashMap<String, Service>();
    private static Entreprise instanceUnique = new Entreprise();
    private static IFactory factoryService;
    private Entreprise() {} //tous les constructeurs au niveau à private

    public static Entreprise getInstance(IFactory factory) {
        factoryService = factory;
        return instanceUnique;
    }
public interface IFactory {
    Service creerService(String nom, String type);
}

public class Factory implements IFactory {

    @Override
    public Service creerService(String nom, String type) {
        if (type.equals("Administratif"))
            return new ServAdministratif(nom);
        else if (type.equals("Technique"))
            return new ServTechnique(nom);
        else
            throw new IllegalArgumentException ("type");
    }

}